Question

Describe briefly the four major groups of Protozoa.

Answer 1

(a)  Amoeboid protozoa:

These organisms live in fresh water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine forms have silica shells on their surface. Some of them such as Entamoeba are parasites.

(b) Flagellated protozoa:

The members of this group are either free-living or parasitic. They have flagella. The parasitic forms cause diseases such as sleeping sickness.

Example: Trypanosoma.

(c) Ciliated protozoa:

These are aquatic, actively proving organisms because of the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. The co-ordinated movement of rows of cilia causes the water laden with food to be steered into the gullet.

Example: Paramecium

(d) Sporozoans: 

This includes diverse organisms that have an infectious spore-like stage in their life cycle. The most notorious is Plasmodium which causes malaria which has a staggering effect on human population.

Answer 2

There are 4 major groups of protozoa.

(1) Amoeboid protozoans or sarcodines

They are unicellular, jelly-like protozoa found in fresh or seawater and in moist soil. Their body lacks a periplast. Therefore, they may be naked or covered by a calcareous shell. They usually lack flagella and have temporary protoplasmic outgrowths called pseudopodia for locomotion. These pseudopodia or false feet help in movement and capturing prey. They include free-living forms such as Amoeba or parasitic forms such as Entamoeba.

(2) Flagellated protozoans or zooflagellates

They are free-living, non-photosynthetic flagellates without a cell wall. They possess flagella for locomotion and capturing prey. They include parasitic forms such as Trypanosoma, which causes sleeping sickness in human beings and free-living forms such as Noctiluca.

(3) Ciliated protozoans or ciliates

They are aquatic individuals that form a large group of protozoa. Their characteristic features are the presence of numerous cilia on the entire body surface and the presence of two types of nuclei. All the cilia beat in the same direction to move the water-laden food inside a cavity called gullet. They include organisms such as Paramaecium, Vorticella etc.

(4) Sporozoans

They include disease-causing endoparasites and other pathogens. They are uninucleate and their body is covered by a pellicle. They do not possess cilia or flagella. They include the malaria-causing parasite Plasmodium.